A new mouse model that better represents chronic infection with hepatitis B virus (HBV) in humans may lead to more effective antiviral therapies for HBV, according to investigators.
During human infection, HBV genomes take the form of covalently closed circular DNA (cccDNA), a structure that has thwarted effective antiviral therapy and, until now, creation of an accurate mouse model, reported lead author Zaichao Xu, PhD, of Wuhan (China) University and colleagues.
“As the viral persistence reservoir plays a central role in HBV infection, HBV cccDNA is the key obstacle for a cure,” the investigators wrote in Cellular and Molecular Gastroenterology and Hepatology.
Although several previous mouse models have approximated this phenomenon with recombinant cccDNA-like molecules (rcccDNA), the present model is the first to achieve genuine cccDNA, which does not naturally occur in mice.
“Although rcccDNA supports persistent viral replication and antigen expression, the nature of rcccDNA may differ from authentic cccDNA, as additional sequences, like LoxP or attR, were inserted into the HBV genome,” the investigators noted.
The new model was created by first constructing an adeno-associated virus vector carrying a replication-deﬁcient HBV1.04-fold genome (AAV-HBV1.04). When injected into mice, the vector led to cccDNA formation via ataxia-telangiectasia and Rad3-related protein (ATR)–mediated DNA damage response, a finding that was confirmed by blocking the same process with ATR inhibitors.
Immediately after injection, mice tested positive for both hepatitis B e antigen (HBeAg) and hepatitis B surface antigen (HBsAg), with peak concentrations after either 4 or 8 weeks depending on dose. HBV DNA was also detected in serum after injection, and 50% of hepatocytes exhibited HBsAg and hepatitis B core protein (HBc) after 1 week. At week 66, HBsAg, HBeAg, and HBc were still detectable in the liver.
“The expression of HBc could only be observed in the liver, but not in other organs or tissues, suggesting that the AAV-HBV1.04 only targeted the mouse liver,” the investigators wrote.
Further experimentation involving known cccDNA-binding proteins supported the similarity between cccDNA in the mouse model and natural infection.
“These results suggested that the chromatinization and transcriptional activation of cccDNA formed in this model dose not differ from wild-type cccDNA formed through infection.”
Next, Dr. Xu and colleagues demonstrated that the infected mice could serve as a reliable model for antiviral research. One week after injection with the vector, mice were treated with entecavir, polyinosinic-polycytidylic acid (poly[I:C]), or phosphate-buffered saline (PBS; control). As anticipated, entecavir suppressed circulating HBV DNA, but not HBsAg, HBeAg, or HBV cccDNA, whereas treatment with poly(I:C) reduced all HBV markers.
“This novel mouse model will provide a unique platform for studying HBV cccDNA and developing novel antivirals to achieve HBV cure,” the investigators concluded.
The study was supported by the National Natural Science Foundation of China, the Fundamental Research Funds for the Central Universities, Hubei Province’s Outstanding Medical Academic Leader Program, and others. The investigators reported no conflicts of interest.